As the demand for increasing transmission rates of radio communication grows, techniques that make effective use of the finite frequency range to increase transmission rates are being widely studied. One of such techniques to increase transmission rates is MIMO (Multiple-Input Multiple-Output) transmission technology. In the MIMO transmission technology, a radio transmitter uses multiple transmit antennas to transmit different streams of data using the same frequency channel. A radio receiver uses multiple receive antennas to receive spatially multiplexed data and separates the data by signal processing. This can increase the transmission rate without broadening the frequency bandwidth.
In order to improve reception characteristics in the MIMO transmission technology, a number of receiving schemes that separate spatially multiplexed signals have been proposed. Known examples include ZF (Zero-Forcing), MMSE (Minimum Mean Square Error), MLD (Maximum Likelihood Detection), and iterative decoding.
The receiving schemes using iterative decoding can be classified as parallel interference canceller (PIC) which removes interference components from a received signal in parallel or as successive interference canceller (SIC) which successively removes interference components from a received signal and demodulates the signal. T. Ohgane et al., “A study on a channel allocation scheme with an adaptive array in SDMA”, IEEE 47th VTC, pp. 725-729, vol. 2 (1997) discloses a parallel interference canceller.
These approaches can be further classified as hard canceller or soft canceller. The hard canceller makes hard decision on a tentative decision result in the course of iterative decoding; the soft canceller uses a soft decision value as a tentative decision result. The hard canceller has an advantage that the hard canceller can make the circuit size smaller than the soft canceller because of its circuit configuration.